1. Field of the Invention
The present invention relates to a cylinder liner and a cylinder block enclosing-casting a cylinder liner therein to be used in an engine, and a process for the preparation of the cylinder liner.
2. Description of the Related Art
A cast iron cylinder block for an engine which has been put to practical use is prepared by enclosing a cast iron cylinder liner in a cylinder block main body by enclosing-casting method in order to reduce the weight and fuel consumption.
However, in the production by a conventional cylinder block having a cast iron cylinder liner, gaps or voids are occasionally formed at the interface between the cylinder block main body and the cylinder liner.
In case gaps are formed at the interface between the cylinder block main body and the cylinder liner, a thermal conductivity therebetween reduces to influence the cooling performance of the engine and to bring about variation of the thermal conductivity in the cylinder liner in the circumferential direction. The circumferential variation of the thermal conductivity of the cylinder liner causes the thermal conductivity of the cylinder liner to vary depending on the circumferential position. The variation of the thermal conductivity causes the cylinder liner not to expand with keeping a perfect circular shape, which results in that inner surface of the cylinder bore is deformed to have a distorted cylindrical shape. When a piston reciprocatingly moves in the deformed cylinder bore, the friction coefficient between the piston and the cylinder liner increases. Therefore, engine oil consumption and abrasion of the piston ring increase, which becomes factors for increased fuel consumption, reduced performance, and reduced durability of the engine.
Further, when water penetrates into the gap formed at the interface between the cylinder liner and the cylinder block main body, the cylinder liner suffers from rust development, which occasionally leads to deformation of the cylinder liner.
Furthermore, if there are gaps at the interface between the cylinder block main body and the cylinder liner enclosed therein by casting, when the inner surface of the cylinder bore is subjected to a machining process, elastic deformation, so-called spring-back of the cylinder liner occurs owing to load generated on processing of the cylinder liner to reduce processing accuracy of the cylinder liner. Moreover, the existence of the gaps at the interface repeatedly gives load to the cylinder liner, and therefore the cylinder liner is apt to be deformed with the passage of time. Similarly, when the thin portion of the cylinder block main body is processed by a machine, a load generated on the processing causes elastic deformation whereby the processed accuracy of the cylinder block is reduced.
An aluminum cylinder block is formed by casting a molten aluminum alloy around a cylinder liner. In the solidification and shrinkage of the molten aluminum alloy, the interface between the cylinder liner and the cylinder block main body receives large load generated by the residual stress mainly of the aluminum alloy and by the difference of thermal expansion ratio between the aluminum alloy and iron for the cylinder liner. In this case, when there are gaps formed at the interface between the cylinder liner and the cylinder block main body, the stress is concentrated in a portion around the gap, whereby the aluminum alloy cylinder block main body is damaged. Particularly, a thin portion of the cylinder block main body is apt to be damaged by concentration of the stress.
To solve the above-mentioned problem, known is a process for the preparation of cylinder block wherein a shot blasting is carried out with respect to the outer surface of the iron cylinder liner by using fine particles of steel, for activating the surface and for obtaining a rough surface. An aluminum cylinder block enclosing-casting the resultant cylinder block acquires excellent closely contact at the interface between the cylinder liner and the cylinder block main body.
As are disclosed in Japanese Kokai Publications No. 2001-227403, No. 2001-334357, and No. Hei-7(1995)-139419, known is a process for the preparation of cylinder block wherein a great number of grooves or protrusions is integrally formed on the surface of the cast iron cylinder liner, and the cylinder liner and the cast cylinder block main body are closely contacted with each other through their contact at interface therebetween.
Furthermore, in another known process for preparing a cylinder block, a Cu-based metal and Zn-based metal, which has good melting adhesiveness with the molten aluminum alloy, is applied to the cylinder block by plating, and a gas component such as hydrogen contained in the plated layer is removed by immersing the cylinder liner in a flux bath, and then the treated cylinder liner is enclosed in the cylinder block main body by enclosing-casting method. Thus, the cylinder liner and the cast cylinder block main body are closely contacted with each other through their contact at interface therebetween.